Hello, and thanks =).
Looks like you were close the first time. Only the font alignment was just a tad off. I remember having to play with alignment a lot to get it right for each resolutions. I remember on every other resolution, I had to fix the alignment by adjusting the background image to get a better result. Now I can't seem to find what value I changed in the theme.plist. Maybe it was just device_pos_y, try increasing that from 70% to move it down, or reduce it to move it up. It may be that the text distance from the device icon is unchangeable and the way to put any distance in between was artificially by making either the device icon png bigger (by giving it a big transparency area). I hope this makes sense.
As for the background, assuming it's outputting at 2460x1440 (does it? I thought this was not a vesa standard). If it is, then maybe the background image simply isn't an adequate size. I can maybe provide you with a 2560x1440 source background image ,which you can then play with... hmm.
Also, I see you have multiple Mac versions running. Cham these days has support, so it's possible to have a different icon for different OS X versions, as seen by my LoginToLion theme. I realize this may facilitate not needing the device names at all. However I'd have to update this theme with new icons, and I don't know if there's enough interest... However.. I can get obsessed about these things =P. An easy way to bring support is for me to simply change the fake text in the device icons. That way I don't really have to create new icons, simply churn out ones that say 10.4/5/6/7/8.